1. Field of the Invention
The present invention relates to a starter motor for cranking an internal combustion engine, the starter motor having a seal member disposed at a front end of a housing.
2. Description of Related Art
A starter motor in which a pinion shaft is supported by a bearing fixed to an end of a housing and a pinion is positioned outside the bearing has been known hitherto. An example of such a starter motor is disclosed in JP-U-2-96471. A relevant portion of such a conventional starter motor is shown in FIG. 4. A ball bearing 110 having an inner ring 111, an outer ring 112 and bearing balls 114 is disposed at an end of a housing 100. A pinion shaft 120 having a pinion 130 at its end is rotatably supported by the ball bearing 110. The pinion shaft 120 is supported slidably in its axial direction. A seal member having a circular wall portion 141 and a lip portion 140 is mounted outside the ball bearing 110. The lip portion 140 slidably contacts the rotating pinion shaft 120 thereby to prevent water or other foreign particles from entering into the housing 100.
As shown in FIG. 4, there is a certain space between the ball bearing 110 and the circular wall 141. Therefore, the seal member tends to move in the axial direction when the seal member is not firmly fixed to the housing 100. When the seal member moves toward the ball bearing 110, its circular wall portion 141 abuts a seal plate 113 disposed between the inner ring 111 and the outer ring 112 of the ball bearing 110. The seal plate 113 is pushed inwardly by the circular wall portion 141, and thereby the balls 114 of the bearing 110 are also pushed. This generates a friction in the ball bearing 110, and thereby the function of the ball bearing 110 is adversely affected. Further, if the seal member moves inwardly, a space between the seal member and the housing 100 is formed, and foreign particles may enter into the housing 100 through that space. This means that a sufficient sealing function may not be secured.